The present invention relates to a process for preparing an aqueous dispersion of polymeric microspheres.
Aqueous dispersions of polymeric microspheres having a particle size in the range of from 1.1 μm to 25 μm are useful in compositions that form coatings with a matte (low gloss) finish, for example, as a clear top coat for leather that is smooth to the touch. The preparation of such dispersions are described in U.S. Pat. No. 7,829,626.
Preparing these aqueous polymeric microspheres with excellent particle size uniformity and a minimum formation of particles in the range of from 20 nm to 500 nm (fines) remains a challenge. The presence of fines above threshold levels results in the formation of unacceptable levels of gel, which requires arduous removal, thereby increasing batch times; in many instances, batches have to be discarded entirely.
US 2017/0058116 (Ando) discloses a method for producing microspheres by suspension polymerization with reported excellent dispersion stability, but requires an extra step of preparing cellulose functionalized small particles, which are adsorbed to the surface of the microspheres to provide such stability. Moreover, Ando's examples all report coefficients of variation in the range of 32% to 50%. It would therefore be advantageous to discover a method that produces monodisperse microspheres with acceptably low production of gel, and that does not require the presence of small particles adsorbed to the surface of the microspheres.